A. Field of the Invention
The present invention relates to a blow-molding apparatus for molding hollow articles made of synthetic resin and, more particularly, to an apparatus which can mold not only bottles of ordinary shapes, but also hollow articles of complex shapes, such as tanks, bent pipes, bent ducts, and double-walled cases.
B. Description of the Prior Art
Hollow articles of synthetic resin, such as bottles and tanks, made by the typical blow molding method, and an apparatus for molding such hollow articles, are disclosed in, for example, Japanese Patent Publication No. 45-31397. Hollow, double-wall articles, such as attache cases and cases for musical instruments, are disclosed in, for example, Japanese Patent Publication No. 49-18748. Further, apparatuses for manufacturing long pipes and long vessels are known.
The apparatuses described in the preceding paragraphs are suitable for manufacturing bottles, tanks, hollow, double-wall articles, long pipes, or the like. However, in order to produce hollow articles, such as pipes, ducts and bottles, which are bent in a complex way, these apparatuses require the assistance of handwork for guiding a parison from a nozzle into the bent cavity of a metal mold.
Recently an apparatus has been developed which can manufacture long, bent, tubular articles, such as bent pipes and bent ducts, without forming flashing or burrs. This apparatus is disclosed in Japanese Patent Disclosure (Kokai) No. 55-21239. The apparatus comprises an extruder having a die head, two lower mold halves attached to a turntable, and a mold opening/closing device. The lower mold halves can be moved between a position below the die head and another position below the mold opening/closing device. A parison is supplied from the extruder into the bending groove cut in the lower mold half. While the parison is being supplied into the groove, the motor for moving the die head is controlled, thereby moving the die head back and forth, and left to right and vice versa, in a horizontal plane, and also up and down such that the distance between the die head and the bottom of the groove is maintained constant. Thus, with this apparatus, it is possible to guide a parison smoothly into the bending groove cut in the lower mold half.
In the apparatus, however, a great power is required to drive the turntable and to move the die head. The apparatus also needs drive mechanisms for rotating the turntable and for moving the die head, and is complicated in structure and inevitably has a large body. In addition, the die head should be moved with high precision in order to guide the half-molten parison from the nozzle, and smoothly through the bending groove. Hence, the apparatus should be equipped with a control device for controlling the die head, and this is inevitably expensive.
Japanese Patent Disclosure (Kokai) No. 53-56262 discloses a molding apparatus wherein a horizontal nozzle for extruding a parison is completely fixed, and a lower mold is moved back and forth, and left to right and vice versa, in a horizontal plane, and also up and down, thereby guiding a parison into the bending groove cut in the lower mold. While the lower mold is moved up and down, the distance between the die head and the bottom of the groove is maintained constant. Since the nozzle is arranged horizontally, the half-molten parison will likely flow downward as soon as it is extruded from the nozzle, whereby its wall fuses before the blow-molding is started. Further, it takes much time to set the lower mold in the correct starting position before the parison is supplied into the complicatedly-shaped groove of the lower mold. In addition, with this apparatus, a parison cannot be efficiently guided through the mold groove.
In the apparatus described above, the mold groove also extends horizontally. Therefore, that portion of the parison which contacts the groove wall for a longer time hardens more quickly than the other portion. Consequently, the parison as a whole does not expand uniformly when pressurized air is blown into it, and the resultant blow-molded article fails to have a uniform wall thickness.